1. Field of the Invention
Embodiments disclosed herein generally relate to a process of depositing a transparent conductive oxide layer over a substrate.
2. Description of the Related Art
Photovoltaic (PV) devices or solar cells are devices which convert sunlight into direct current (DC) electrical power. PV or solar cells typically have one or more p-n junctions. Each junction comprises two different regions within a semiconductor material where one side is denoted as the p-type region and the other as the n-type region. When the p-n junction of the PV cell is exposed to sunlight (consisting of energy from photons), the sunlight is directly converted to electricity through the PV effect. PV solar cells generate a specific amount of electric power and cells are tiled into modules sized to deliver the desired amount of system power. PV modules are created by connecting a number of PV solar cells and are then joined into panels with frames and connectors.
Several types of silicon films, including microcrystalline silicon (μc-Si), amorphous silicon (a-Si), polycrystalline silicon (poly-Si) and the like, may be utilized to form PV devices. A transparent conductive film, sometimes referred to as a transparent conductive oxide (TCO) may be used as a top surface electrode disposed on the top of the PV solar cells. Furthermore, the TCO layer may be disposed between a substrate and a photoelectric conversion unit as a contact layer. The TCO should have high optical transmittance in the visible or higher wavelength region to facilitate transmitting sunlight into the solar cells without adversely absorbing or reflecting light energy. Additionally, low contact resistance and high electrical conductivity of the TCO are desired to provide high photoelectric conversion efficiency and electricity collection. A certain degree of texture or surface roughness of the TCO is also desired to assist sunlight trapping in the films by promoting light scattering. Overly high impurities or contaminant of the TCO often result in high contact resistance at the interface of the TCO and adjacent films, thereby reducing carrier mobility within the PV cells. Furthermore, insufficient transparency of the TCO may adversely reflect light back to the environment, resulting in a diminished amount of sunlight entering the PV cells and a reduction in the photoelectric conversion efficiency.
Therefore, there is a need for an improved method for fabricating a TCO.